Usually, as shown in FIG. 1, a vacuum interrupter comprises a vacuum container (1) closed with end plates (21), (22), a pair of electrodes (30), (40) facing to each other and conductive rods (5), (6) provided through said end plates (21), (22) and in which a bellows (7) is mounted on one electrode rode (6) to be movable in the axial direction without affecting air-tightness, and said electrodes (30), (40) are relatively movable and can be brought into contact with each other. Further, a shield (8) is provided to have deposited thereupon any evaporated metals. Said conductive rod (6) is driven by a drive mechanism not shown for switching operation of an electric circuit.
In such type of vacuum interrupter, it is well known that interruption performance can be improved by stably and uniformly distributing the arc on the surfaces of the electrodes by applying a magnetic field in parallel to the arc, particularly when interrupting a large current arc. It is also known that when said electrodes (30), (40) are in a closed state, an electro-magnetic repulsive force is generated due to the large current application, and a small gap is formed between said electrodes (30), (40), thereby generating a local arc which brings about welding or deteriorates the electrode surfaces, finally lowering withstand voltage performance.
To meet the aforesaid interruption of large current arc and to reduce the electro-magnetic repulsive force when applying a large current, a further vacuum interrupter has been proposed as shown in FIG. 2(a)-(c) (Japanese laid-open Patent Publication (unexamined) No. 57-3327). FIG. 2 (a) is a side view showing an example of arrangement of electrodes in such a prior vacuum interrupter, FIG. 2 (b) is a plan view in the direction of the arrow b--b in FIG. 2 (c), and FIG. 2 (c) is a plan view in the direction of the arrow c--c in FIG. 2 (a). In these drawings, reference numerals (50), (60) designate bridge conductors respectively fixed on the ends of the conductive rods (50), (60). These bridge conductors (5), (6) are rectangular and projecting parts (51), (52), (61), (62) are respectively formed on both ends thereof. Numerals (30), (40) designate a pair of electrodes connected electrically to each bridge conductor (50), (60) on their outer peripheral back sides respectively. As shown in FIG. 2 (b), (c), circular arc-shaped grooves (33), (34), (43), (44) serving as high resistance areas are formed on each electrode (30), (40) by cutting at required distances. Thus circular arc-shaped electrode parts (31), (32) and (41), (42) serving as outside parts of the electrodes partitioned by these grooves (33), (34) and (43), (44) are formed in the electrodes (30), (40). Said bridge conductor (50) is so arranged as to cross the grooves (43), (44), and the projecting parts (51), (52) and (61), (62) are electrically and mechanically connected to substantially middle parts of said circular arc-shaped electrode parts (31), (32) and (41), (42).
Gaps between said bridge conductors (50), (60) and the electrodes (30), (40) are desired to be as small as possible, but it is necessary that the gaps are in a range in which the electrodes (30), (40) do not come in contact with the bridge conductors (50), (60) when the electrodes are butted to each other which would bring about elastic deformation due to an applied mechanical force. The aforesaid electrode (30) and the bridge conductor (50) are respectively of the same configuration as the electrode (40) and the bridge conductor (60), but the electrode (40) and the bridge conductor (60) are so arranged as to face to the electrode (30) and the bridge conductor (50) being respectively turned by 90.degree. therefrom.
According to this prior art, when an opening operation is performed by an operation mechanism not shown, an arc is formed between the electrodes (30), (40). In this step, when a current i flows from the conductive rod (5) toward the conductive rod (6), an arc is formed between a point A of the electrode (30) and a point A' of the electrode (40), the current i passes from the conductive rod (5) to the arc point A by way of the bridge conductor (50), the projecting part (51) thereof, the circular arc-shaped part (31) of said electrode (30) and through a gap B between the grooves (33), (34). That is, almost one turn is formed by a current loop (5).fwdarw.(50).fwdarw.(51).fwdarw.(31).fwdarw.B.fwdarw.A. Since the (51).fwdarw.(31).fwdarw.B.fwdarw.A is a loop formed by the electrode itself, the loop is near the point A of the arc and a strong axial magnetic field is generated. In the same manner, the current i passes from the point A' of the other electrode (40) to the conductive rod (6) by way of a gap C between the grooves (43), (44) of the electrode (40), the circular arc-shaped electrode part (41), the projecting part (61) and the bridge conductor (60). That is, one turn is further formed by a current loop A'.fwdarw.C.fwdarw.(41).fwdarw.(61).fwdarw.(60).fwdarw.(6), and a magnetic field of the same axial direction as the foregoing loop is generated. Thus, a strong combined magnetic flux in the axial direction acts in parallel to the arc A--A' as indicated by the arrow .PHI. in FIG. 2(a), effectively preventing emission and diffusion of ionized metals from the arc to outside, acquiring a sufficient amount of plasma particles and stabilizing the arc. In the event that an accidental large current should flow in the closed state, an electro-magnetic repulsive force is generated at contact points due to concentration of the current and acts to separate the electrodes (30), (40), but since the current direction from the projecting part (51) to the gap B in the electrode (30) is same as that from the gap C to the projecting part (61) in the other electrode (40), the circular arc-shaped electrode parts (31), (41) are strongly attracted to each other. Actually, in the closed state of said electrodes (30), (40), a lot of contact points are distributed in the electrode surfaces and a quite strong electro-magnetic attractive force is generated on all areas of the circular arc-shaped electrode parts (31), (32) and (41), (42), and therefore the electro-magnetic repulsive force due to the current concentration at the contact points is effectively offset.
Thus, the electrode contact force applied to said electrodes (30), (40) can be greatly reduced by means of the operation mechanism not shown, and and the operation mechanism can be small-sized and light-weight.
According to the prior vacuum interrupter arranged as above, however, a serious problem exists in that, in the arc formed between the electrodes (30), (40), when the arc current is so large as to extend to the high resistance areas, i.e., the areas near the grooves (33), (34), (43), (44), the one turn cannot be formed by the current loop and the magnetic field necessary for the stable and uniform distribution of the arc is not generated, either. Moreover, another problem exists in that eddy current is generated inside the electrode section surrounded by the grooves (32), (34) or (43), (44) inhibiting thereby generation of an effective axial magnetic filed.
It is, therefore, an object of the present invention to overcome the above-discussed problems of the conventional vacuum interrupter and to provide a novel vacuum interrupter, in which one turn is formed by an electric current loop generated in the electrodes, and a strong axial magnetic field can be generated while interrupting eddy current passage.